A new sphenodontian (Lepidosauria: Rhynchocephalia) from the Late Triassic of Argentina and the early origin of the herbivore opisthodontians

Abstract

Sphenodontians were a successful group of rhynchocephalian reptiles that dominated the fossil record of Lepidosauria during the Triassic and Jurassic. Although evidence of extinction is seen at the end of the Laurasian Early Cretaceous, they appeared to remain numerically abundant in South America until the end of the period. Most of the known Late Cretaceous record in South America is composed of opisthodontians, the herbivorous branch of Sphenodontia, whose oldest members were until recently reported to be from the Kimmeridgian-Tithonian (Late Jurassic). Here, we report a new sphenodontian, Sphenotitan leyesi gen. et sp. nov., collected from the Upper Triassic Quebrada del Barro Formation of northwestern Argentina. Phylogenetic analysis identifies Sphenotitan as a basal member of Opisthodontia, extending the known record of opisthodontians and the origin of herbivory in this group by 50 Myr.

Taxonomic reassessment ofClevosaurus latidensFraser, 1993 (Lepidosauria, Rhynchocephalia) and rhynchocephalian phylogeny based on parsimony and Bayesian inference

“…Indeed, we recovered F. latidens as the earliest diverging taxon within Opisthodontia. This clearly confirms that F. latidens is not referable to the genus Clevosaurus, and supports the erection of a new opisthodontian genus, as previously suggested (Jones, 2006a(Jones, , 2009Martínez et al, 2013;Hsiou et al, 2015;Klein et al, 2015). Within Opisthodontia, the relationships of eilenodontines are quite well resolved; our results only differ from the works of Martínez et al (2013) and Cau et al (2014) in finding Ankylosphenodon outside of Opisthodontia.…”

“…Another major difference compared to the previous analyses of Martínez et al (2013) and Hsiou et al (2015) is that the Triassic taxon Pelecymala was no longer recovered as closely related to Opisthodontia, but was found in a polytomy with early-diverging rhynchocephalians such as Rebbanasaurus Evans, Prasad, and Manhas, 2001, the clade of Sphenocondor Apesteguía, Gomez, andRougier, 2012 andGodavarisaurus Evans, Prasad, andManhas, 2001, and the clade Eusphenodontia.…”

“…The strict consensus tree of the second analysis of Cau et al (2014) also found Derasmosaurus, Oenosaurus, and Zapatadon in a similar polytomy, and forming the sister group of the clade comprising Sphenodon, Cynosphenodon, Sphenovipera, Kawasphenodon Apesteguía, 2005, and Theretairus. The close relationship of Sphenovipera and Theretairus has been constantly recovered in previous analyses (e.g., Martínez et al, 2013;Hsiou et al, 2015).…”

“…In contrast to the Chinese specimens, the referral of 'C. latidens' to Clevosaurus has been widely questioned (Jones, 2006a(Jones, , 2009Martínez et al, 2013;Hsiou et al, 2015;Klein et al, 2015).…”

Guelb el Ahmar (Bathonian, Anoual Syncline, eastern Morocco): First continental flora and fauna including mammals from the Middle Jurassic of Africa

“…Rhynchocephalians were present as early as the Triassic in Europe, North America, Madagascar and South America (Evans et al, 2001;Martínez et al, 2013). They achieved a more cosmopolitan distribution during the Early Jurassic, adding Asia, Africa and India (Kota Fm) to their range.…”